John F. Kennedy’s only surviving sibling, 85-year-old Jean Kennedy Smith, laid a wreath at her brother’s grave Friday and accompanied 10 Kennedy family members as they prayed and left roses to commemorate the 50th anniversary of his ­assassination.

A few hundred people attended the morning ceremony at Arlington National Cemetery in Virginia, which lasted only a few minutes and had no spoken words, while a bugler played taps.

About an hour earlier, Attorney General Eric Holder paid his respects at the grave, where the Eternal Flame was restored last year ­after renovations and repairs. Holder bowed his head and placed a Justice Department commemorative coin at the site.

In Boston, a musical tribute featuring singer-songwriter James Taylor and a Marine Corps Band was held at the John F. Kennedy ­Library and Museum.

Thousands line up for the JFK ceremony in Dealey Square in Dallas.

Massachusetts Gov. Deval Patrick read an excerpt from the speech Kennedy gave when he accepted the Democratic presidential nomination in Los Angeles in July 1960.

“The new frontier of which I speak is not a set of promises, it is a set of challenges. It sums up not what I intend to offer the American people, but what I intend to ask of them,” Patrick recited.

During the day, a stream of visitors came in to view the museum’s artifacts, including a video of Kennedy’s state funeral and a display of the saddle, sword and boots borne by Black Jack, the riderless horse who led the procession before Kennedy’s burial.

Hundreds of visitors also lined up at the museum to write their thoughts and names in four large guestbooks set up on pedestals decorated with flowers.

Among the visitors to the grave at Arlington was Wallace Johnson, 74, and other veterans of the US Army Special Forces.

Johnson, of Dumfries, Va., said Kennedy holds a special place in the hearts of Special Forces members, noting that the president had given his instant approval to the group’s iconic green beret on a 1961 visit to Fort Bragg, NC.

“He authorized that headgear right on the spot,” said Johnson, who left a green beret at Kennedy’s grave on Friday.

In the Berlin neighborhood where Kennedy made his celebrated “Ich bin ein Berliner” speech, a crowd attended another wreath-laying ceremony.

In Dublin, a half-dozen Irish soldiers formed a guard of honor outside the US Embassy as the American flag was lowered to half-staff in honor of the Irish-American president.

More than a dozen retired Irish army officers — who as teen ­cadets had formed an honor guard at Kennedy’s graveside — gathered in the front garden of the embassy while Irish Foreign Minister Eamon Gilmore and embassy staff observed a minute’s ­silence.

“We were young guys, all pretty much 18. We had no passports, no visas. None of us had flown before,” recalled one of the former cadets, Brian O’Reilly, 68.

“We were told on the Saturday night we were wanted for the funeral. The next day, we were on the plane with our own president [Eamon de Valera] heading for Washington.”

The suburban Buffalo high school that was the first in the nation to be named after Kennedy showed video of the president in the morning and observed a moment of silence in the afternoon.

When the newly opened John F. Kennedy HS in Cheektowaga was named in 1962, it was the first public school in the United States to be named for a sitting president. Later that year, JFK was visiting Buffalo when he first learned of what would be known as the Cuban missile crisis.